Semiconductor image sensors are used to sense radiation such as light. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) and charge-coupled device (CCD) sensors are widely used in various applications such as digital still camera or mobile phone camera applications. These devices utilize an array of pixels in a substrate, including photodiodes and transistors, that can absorb radiation projected toward the substrate and convert the sensed radiation into electrical signals.
In recent years, the semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. As a part of the IC evolution for semiconductor image sensors, the size of the radiation-sensitive pixels has been steadily reduced. As the pixels and the separation between adjacent pixels continue to shrink, issues such as excessive dark current and cross-talk become more difficult to control. Conventional methods of addressing the dark current and cross-talk issues have been expensive and require complex implementation. Even then, the image sensors fabricated using conventional methods may still have poor dark current and cross-talk performance.
Therefore, while existing semiconductor image sensors have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.